Awesome post Zapped, I totally agree. If it uses a carto, it's a tank. If it uses a wick and coil head, like a Kanger Protank, Vivi Nova, etc it's just a clearo. Calling a clearo a tank confuses many people that don't know any better.
OP,
There is no way possible to determine which one will last longer. Some people run 10ml of juice through a carto and toss it, I personally get around 30ml through a carto (while in a tank) before I consider tossing it. Cartos will last longer in a properly functioning tank than they would normally, because they are kept wet at all times. Different cartos will last different amounts of time, your vaping habits will change how long you can use a carto, the juice will effect the lifetime, what power you are running at, and when you device to change it.
A carto very rarely just stops working. You could probably vape a single carto for a year, but the draw would be super tight, the coil would be gunked to hell and taste awful, and the filler material could clog up from using certain juices. It's up to you to decide when a carto needs replacing.
Coil heads on clearos are basically the same way, but you do have the option to dry burn the coil head, which can extend the life of it quite a bit. You can also rebuild the coil heads yourself with some new wire and wick.
As for the tank body and clearo body, leaks are generally a result of damaged o-rings. Most tanks out today have extra o-rings available for them on a few sites, some places like IBtanked will even give you a full set of replacement o-rings when you order a tank.
With a tank, inserting cartos over and over can damage the internal o-rings that seal against the carto, This is the most common reason tanks leak, and can be prevented by using a tank filling tool which will give a smooth gradual slope for the o-rings to stretch around the carto, instead of pushing the sharp edge of the carto straight into it.
Clearos come in all shapes, sizes, and designs, some leak, some don't. I have yet to find ANY clearo that didn't leak, from Vision "stardusts" Vivi Novas, Kangers, I've nearly tried them all. Every single one would either leak down the center tube, or leak where the base or top screws on.
I've never had a leaky tank, one of many reasons I hate clearos and love cartos.